The invention relates to a silicone emulsion and to a method of making the silicone emulsion. A process is described in which a particular sequence of manipulative steps has been found to produce certain emulsion compositions possessing a particle size of silicone in the emulsion in the range of one to one hundred microns, in contrast to processes in which the particle size of the silicone in the emulsion has been limited to less than about 0.35 microns.
A process for making polysiloxane emulsions is described in copending U.S. patent application Ser. No. 07/844067 filed Mar. 2, 1992, which is a continuation of U.S. patent application Ser. No. 07/534827 filed Jun. 7, 1990 and now abandoned. The parent application has been published as European Patent Application Publication Number 0 463 431 A2 on Jan. 2, 1992. Each of the three applications are assigned to the same assignee as the present invention.
In the process according to the copending prior application, a silicone oil-in-water emulsion is formed mechanically by forming initially a thick phase emulsion by combining and shearing the silicone, a nonionic surfactant having an HLB value of 10-19, and water. To the thick phase emulsion there is subsequently added another nonionic surfactant but one having an HLB value of 1.8-15.0, together with optional anionic and cationic surfactants. The mixture is sheared to reduce the particle size of the silicone oil in the emulsion to less than 0.35 microns (350 nanometers), and water is added to provide a content of silicone in the emulsion of 1-60 percent by weight.
While such techniques have been found to be effective, the application of these silicone emulsions in personal care applications is limited due to the small particle size of the silicone in the emulsion. According to the present invention, a similar technique has been discovered but which possesses the advantage of producing emulsions better suited for use in products for the personal care market. Thus, emulsions resulting from the process according to the present invention have a particle size of silicone oil in the emulsion of 1-100 microns in contrast to the emulsions described in the copending application which possess a particle size of less than 0.35 microns.
The basis for making an emulsion is to stabilize the silicone oil in water in which the silicone is insoluble. The oil particles are stabilized by adding surfactants to the system. The choice and amount of surfactants used becomes critical in determining the type of emulsion formed (oil-in-water vs. water-in-oil), the particle size, its uniformity and stability.
The particle size of an emulsion has an effect on the end use. For many applications, emulsions need not be destabilized in order to be effective. For hair care applications, especially for use as conditioners, either in conditioning shampoos or as conditioners in a rinse, the effectiveness of the emulsion depends on the amount of silicone that is deposited on to the hair. The higher the particle size, the faster the destabilization or breaking of the emulsion, thus increasing the deposition of the silicone on the hair.
Blends of a very high viscosity silicone polymer gum, with a low viscosity silicone fluid (5 to 1000 cs) have the advantage over other polymers in giving good conditioning effects. This is due to the fact that by mixing silicone gums with a fluid, the gum can be uniformly spread on the surface in a monolayer, giving good feel and softness to the surface of the substrate (hair). Incorporation of such high viscosity silicones into a shampoo is very difficult and cumbersome. By making an emulsion of the silicone gum/fluid blend, many of the difficulties associated with mixing into a shampoo can be avoided. The emulsion can be simply added to the shampoo and mixed by simple stirring.